1. Field of the Invention
The present invention relates to a control mechanism for a fuel injection pump for a diesel engine, the control mechanism being provided with an electronic governor and a cold start device for advancing injection timing during start of a cold engine. Particularly, the invention relates to the control mechanism which change a base position of a governing rack located by a controller in correspondence to switching on/off of the cold start device.
2. Background Art
Conventionally, there are well-known fuel injection pumps for a diesel engine. Each of the fuel injection pumps comprises a plunger, a plunger barrel, a distribution shaft, and a plurality of delivery valves, wherein the plunger is vertically slid in a plunger barrel so as to discharge pressurized fuel to the distribution shaft, an the distribution shaft sends to the delivery valves for delivering fuel to respective fuel injection nozzles.
Of the fuel injection pumps, there are well-known fuel injection pumps each of which is provided with an electronic governor having a rack actuator which is actuated by a controller so as to control a position of a governing rack (hereinafter, referred to as “rack position”), as disclosed in Japanese Laid Open Gazette No. Hei 10-325339. Due to the actuation of the rack actuator, the rack position is changed in correspondence to pump rotary speed so as to optimize injection quantity.
Of the fuel injection pumps, there is a well-known fuel injection pump provided with a Cold Start Device (hereinafter, referred to as “CSD”) configured so that a draining sub port is formed in the plunger barrel, and a control actuates an injection-quickening actuator for opening and closing the draining sub port so as to change injection timing in correspondence to the rotary speed, as disclosed in Japanese Laid Open Gazette No. 2000-234576. When a cold engine starts to drive, the sub port is closed (i.e., CSD is switched on) so as to advance the injection timing, thereby smoothing facilitating start of the engine.
Depending on detection of engine temperature (temperature of engine cooling water), the controller selects a suitable one from rack position control maps of the electronic governor about engine rotary speed in correspondence to the detected engine temperature. Referring to FIG. 7(a), the map selection depends on the switching on/off of the cold start device, i.e., actuation/disactuation of CSD (the injection-quickening actuator). Each graph of FIGS. 7(a), 8(a) and 9(a) is drawn with pump rotary speed (replaceable with engine rotary speed) X as the x-axis, and with rack position R as the y-axis. The increase direction of rack position R corresponds to the direction for increasing injection quantity. Each of FIGS. 7(b), 8(b) and 9(b) graphs curves of injection quantity Q relative to pump rotary speed (replaceable with engine rotary speed) N, based on the corresponding rack position control map of each of FIGS. 7(a), 8(a) and 9(a).
FIG. 7(a) graphs a rack position control map 91a when the engine is cold (when CSD is switched on), and a rack position control map 91b when the engine is hot (when CSD is switched off). FIG. 7(b) graphs an injection quantity characteristic curve 92a when the engine is cold (when CSD is switched on), and an injection quantity characteristic curve 92b when the engine is hot (when CSD is switched off), curves 92a and 92b being obtained according to respective maps 91a and 91b. When the engine is cold, the rack position is shifted for reducing the injection quantity when the engine is cold (in relative to the same engine (pump) rotary speed, rack position R on graph 91a is smaller than rack position R on graph 91b), however, CSD is switched on for closing the sub port, thereby resulting in increase of the injection quantity (in relative to the same engine (pump) rotary speed, injection quantity Q on graph 92a is larger than injection quantity Q on graph 92b). Conversely speaking, when CSD is switched on, rack position R is shifted for reducing the injection quantity so as to prevent excessive increase of injection quantity.
In each of the rack position control maps, variation pattern of rack position relative to engine (pump) rotary speed is evened particularly in consideration of the hot engine condition. In this regard, on the assumption that CSD is not actuated, as characteristic curve 91b, when the rotary speed is equal to or exceeds a threshold rotary speed N2, rack position R serving as a parameter for the control of injection quantity is fixed to a rated rack position R2. It is now supposed that CSD is not actuated and the rotary speed is smaller than threshold rotary speed N2, i.e., the rotary speed is within an early engine-starting rotary speed range. When the rotary speed varies between 0 and a rotary speed N1 close to threshold rotary speed N2, a rack position R1, as shifted from rack position R2 in the direction for increasing the injection quantity, is selected as the base position for the control of injection quantity on starting of the engine, i.e., a fuel-increasing rack position for engine start, thereby quickly raising the engine rotary speed. As the rotary speed increases from N1 to N2, rack position R selected as the base position for the control of injection quantity moves from rack position R1 in the direction for reducing the injection quantity, and finally reaches rack position R2.
With respect to the exchange of rack position control map depending on the engine temperature (the actuation/disactuation of CSD), variation pattern of the rack position relative to variation of engine rotary speed, such as the curve shape of characteristic curve 91b, is not changed, but the electronic governor controlling gain relative to every engine rotary speed is simply reduced to even degree from the original value. Consequently, as shown in FIG. 7(a), characteristic curve 91a in actuated condition of CSD and characteristic curve 91b in disactuated condition of CSD are shaped as being shifted in parallel from each other along the y-axis. With respect to characteristic curve 91a, while the rotary speed varies within the range of rotary speed that is not smaller than rotary speed N2, a rated rack position R4, which is disposed at a position shifted from rated rack position R2 in the direction for reducing injection quantity, is selected as the base position for the control of injection quantity. While the rotary speed varies within the early engine-starting rotary speed range between 0 and N2, and especially when it varies between 0 and N1, a fuel-increasing rack position R3 for engine start a start, which is lower than rack position R1, is selected as the base position for the control of injection quantity. As the rotary speed within the early engine-starting rotary speed range varies from N1 to N2, a rack position selected as the base position for the control of injection quantity moves in the direction for reducing injection quantity from fuel-increasing rack position R3 for engine start, and finally, when the rotary speed reaches N2, the rack position reaches rated rack position R4.
In correspondence to this rack position control, as shown in FIG. 7(b), characteristic curve 92a of injection quantity of the cold engine (when CSD is actuated) and characteristic curve 92b of injection quantity of the hot engine (when CSD is not actuated) are necessarily shaped as being shifted from each other in parallel along the y-axis. As a result, during low speed rotation of the started cold engine (while CSD is actuated), the injection quantity is still large so as to cause black smoky exhaust gas. In this way, the rack control maps having a fixed variation pattern out of consideration of engine temperature variation restricts optimization of cold engine start and reduction of black smoke in exhaust gas during engine start-up.
To further optimize cold engine start and reduce black smoke in exhaust gas during engine start-up, the characteristic of controlled rack position has to correspond to the respective actuated and disactuated conditions of CSD, especially, by considering the fuel-increasing rack position for engine start.
Further, with respect to the conventional electronic governor, a minimum rack position R9 (for zeroing or substantially zeroing injection quantity) is set so as to prevent reduction of injection quantity from causing stop of the engine during sudden reduction of engine rotary speed.
As shown in FIG. 8(a), only the pump rotary speed is the parameter for setting the minimum rack. That is, a single characteristic curve 93 is set regardless of whether the engine is hot or cold (whether CSD is actuated or disactuated). With respect to the relation between characteristic curve 91a in actuated condition of CSD and characteristic curve 93, a rack position difference (undershoot U1) between rated rack position R3 and minimum rack position R9 is so small as to prevent undesirable influence onto the engine rotary speed. However, with respect to the relation between characteristic curve 91b in disactuated condition of CSD and characteristic curve 93, a rack position difference (undershoot U2) between rated rack position R2 and minimum rack position R9 is larger than undershoot U1, so that when operation for suddenly reducing engine rotary speed is performed in disactuated condition of CSD, the large undershoot U2 causes undesirably large degree of momentary reduction of engine rotary speed. In this regard, FIG. 8(b) graphs characteristic curves 94a and 94b of injection quantity control pattern (N–Q characteristics), which correspond to the minimum rack position pattern (N–R characteristic) shown in FIG. 8(a) adapted to the actuated condition of CSD and to the disactuated condition of CSD, respectively.
Similar to the characteristic curves of FIG. 7(b), characteristic curves 92a and 92b express characteristics of controlled injection quantity without the minimum rack position control for the actuated condition of CSD and for the disactuated condition of CSD, respectively. The problem of undershoot during sudden speed down operation is described as the above. On the contrary, if sudden speed up operation is performed, the problem arises that overshoot becomes so large as to cause undesirably large degree of momentary increase of engine rotary speed.
To reduce the momentary reduction and increase of engine rotary speed, the minimum rack position variation should be set to have characteristics suitable for the actuated condition of CSD and for the disactuated condition of CSD, respectively.
Further, during start of a cold engine, due to the idle-up function of the conventional electronic governor, the low idle rotary speed of the engine is gradually reduced as the engine cooling water is heated.
During work of the idle-up function, as shown in FIG. 9(a), map data expressed as characteristic curve 95 is adapted to correspond to the relation of rack position to accelerator set value (target rotary speed (set value) set when the engine idles). The map data expressed by characteristic curve 95 is used for both the actuated and disactuated conditions of CSD. Namely, the same map data is used whether the CSD is actuated or disactuated.
However, as shown in FIG. 9(b), the injection quantity becomes different depending on whether or not CSD is actuated because the presence or absence of fuel draining depends on whether or not CSD is actuated. Even if the same rack position is set relative to the same accelerator set value regardless of the actuation or disactuation of CSD, actual injection quantity becomes different, i.e., the engine rotary speed becomes different depending whether or not CSD is actuated. Namely, in correspondence to the single map data for controlling injection quantity (engine rotary speed), two different characteristic curves 96a (in actuated condition of CSD) and 96b (in disactuated condition of CSD) about actual engine rotary speed variation are established.
Consequently, when a cold engine started in the actuated condition of CSD is warmed and the actuated CSD is shifted into the disactuated condition, injection quantity is suddenly reduced and the engine rotary speed is suddenly reduced, thereby causing discomfort of an operator.
Therefore, to prevent fluctuation of engine rotary speed in no load (idle) condition, the characteristic curve is required to correspond to the respective actuated and disactuated conditions of CSD.
The present invention takes the above problems into account for setting N–R characteristic curve corresponding to the respective actuated and disactuated conditions of CSD, thereby optimizing start of a cold engine and reduction of black smoke in exhaust gas, and ensuring stable operation of an engine with no fluctuation of engine rotary speed.